Large molecules support cell function.

In living things, there are four main types of large molecules: (1) carbohydrates,
(2) lipids, (3) proteins, and (4) nucleic acids. Thousands
of these molecules work together in a cell. The four types of molecules
in all living things share one important characteristic. They all contain
carbon atoms. These large molecules are made up of smaller parts
called subunits.

Carbohydrates

Carbohydrates are used
for structure and energy
storage. Carbohydrates,
such as cellulose, are
made of sugars.

Carbohydrates (KAHR-boh-HY-DRAYTS) provide the cell with energy.
Simple carbohydrates are sugars made from atoms of carbon, oxygen,
and hydrogen. Inside cells, sugar molecules are broken down. This
process provides usable energy for the cell.

Simple sugar molecules can also be linked into long chains to form
more complex carbohydrates, such as starch, cellulose, and glycogen.
Starch and cellulose are complex carbohydrates made by plant cells.
When a plant cell makes more sugar than it can use, extra sugar
molecules are stored in long chains called starch. Plants also make
cellulose, which is the material that makes up the cell wall. Animals
get their energy by eating plants or other animals that eat plants.

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Lipids

Lipids are the fats, oils, and waxes found in living things. Like
carbohydrates, simple lipids are made of atoms of carbon, oxygen,
and hydrogen and can be used by cells for energy and for making
structures. However, the atoms in all lipids are arranged differently
from the atoms in carbohydrates. Many common lipids consist of
a molecule called glycerol bonded to long chains of carbon and
hydrogen atoms called fatty acids. This structure gives lipids unique
properties. One extremely important property of lipids is that they
cannot mix with water.

Lipids make up the
membranes surrounding
the cell and organelles.
Lipids are made of fatty
acids and glycerol.

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How do cells use carbohydrates and lipids?

Proteins

Proteins are made up
of amino acids. Proteins
carry out most of the
chemical activity in cells.

Proteins are made of smaller molecules called amino acids. Amino
acids contain the elements carbon, oxygen, hydrogen, nitrogen, and
sometimes sulfur. In proteins, amino acids are linked together into
long chains that fold into three-dimensional shapes. The structure and
function of a protein is determined by the type, number, and order of
the amino acids in it.

Your body gets amino acids from protein in food, such as meat,
eggs, cheese, and some beans. After taking in amino acids, your cells
use them to build proteins needed for proper cell functioning. Some
amino acids can be made by the body, but others must be taken in
from an outside food source.

There are many types of proteins. Enzymes are proteins that control
chemical reactions in the cells. Other proteins support the growth and
repair of living matter. The action of proteins in your muscles allows
you to move. Some of the proteins in your blood fight infections.
Another protein in your blood delivers oxygen to all the cells in your
body. Proteins are also important parts of cell membranes. Some proteins
in the cell membrane transport materials into and out of the cell.

Nucleic Acids

Nucleic acids store
and translate the genetic
information a cell needs
to function. Nucleic acids,
such as DNA, are made
up of nucleotides.

Nucleic acids (noo-KLEE-ihk) are the molecules that hold the
instructions for the maintenance, growth, and reproduction of a cell.
There are two types of nucleic acids: DNA and RNA. Both DNA and
RNA are made from carbon, oxygen, hydrogen, nitrogen, and phosphorus.
The subunits of nucleic acids are called nucleotides.

DNA provides the information used by the cell for making
proteins a cell needs. This information takes the form of a code
contained in the specific order of different nucleotides in the DNA.

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The pattern of nucleotides in DNA is then coded into RNA, which
delivers the information into the cytoplasm. Other RNA molecules in
the cytoplasm produce the proteins.